1. Field of the Invention
The present invention relates to an apparatus and method for manufacturing metal filaments, and more particularly to an apparatus and method for manufacturing fine metal filaments from metal bars using a rapid solidification process.
2. Description of the Related Art
Here, xe2x80x9cmetal filamentxe2x80x9d is a fiber having a circular or nearly circular cross section with a diameter of 100 xcexcm or less.
In order to manufacture such a metal fiber, various methods have been used. For example, there are a method for drawing a metal material having a bar or rod shape using a die made of a hard alloy or diamond, a method for cutting a solid metal material to obtain a wire, and a method for extracting molten metal using a nozzle having a small diameter, and solidifying the extracted product. A metal fiber manufacturing method using a rapid solidification process has been used since 1980, taking into consideration the advantages of that process capable of simplifying the manufacturing apparatus while providing a uniformity of fibers. Products obtained in accordance with such a rapid solidification process may have forms of fibers, strips, and ribbons.
For example, U.S. Pat. Nos. 4,290,993, 3,812,901, and 5,015,993 disclose methods for manufacturing filaments by bringing a rotating disk having an indented wheel shape into contact with a molten metal material contained in a vessel such as a hearth or crucible. Similar methods are also disclosed in U.S. Pat. Nos. 5,642,771, 5,601,139, and 4,339,508. That is, they disclose methods for manufacturing metal strips or metal ribbons having a cross section with a rectangular or plate shape, rather than a circular or nearly circular shape, by supplying a molten metal material onto a cooling surface having at least one groove with a certain depth using a nozzle or tube, solidifying the supplied molten metal material while allowing the material to flow, along the groove, toward a disk arranged beneath the cooling surface. In addition, U.S. Pat. Nos. 5,213,151, 4,930,565, 5,345,993, and 4,807,694 disclose methods for manufacturing metal strips using a rotating disk under the condition in which a molten metal material is contained in a vessel such as a hearth or crucible.
However, the above mentioned methods, in which metal fibers are manufactured using a molten metal contained in a vessel have problems of damage of the vessel by heat and a change in composition caused by a reaction of the molten metal with the vessel, because the vessel should receive the molten metal maintained at a high temperature of 1,600xc2x0 C. For this reason, it is impossible to continuously supply molten metal contacting the rotating disk. Furthermore, where molten metal is extracted using a nozzle or tube, it is impossible to manufacture fine products such as fibers. Typically, products having a strip or ribbon shape with a certain width are manufactured by this method.
U.S. Pat. No. 4,946,746 discloses an advanced technique. That is, this patent discloses an apparatus and method for manufacturing metal fibers by injecting a molten metal material into the interior of a rotating drum by use of a nozzle, and solidifying the injected metal material. However, this technique has problems in that when the amount of molten metal to be injected is increased, the amount of the molten metal collect in an entrance of nozzle without being injected is increased, thereby causing a degradation in workability and productivity. Since the molten metal should be injected through the nozzle, it is impossible to obtain metal fibers having a diameter of 70 xcexcm or less.
In order to eliminate drawbacks involved with the methods in which metal fibers are manufactured using a molten metal material contained in a vessel, U.S. Pat. No. 5,027,886 discloses a method for fabrication of metallic fibers by upwardly supplying a metal rod through a vertical opening, and heating to the upper end of the metal rod. In accordance with this method, a metal rod is supplied through a guide. The upper end of the metal rod is melted by an induction coil installed around the upper end of the guide. The molten metal is stored in a collar at the upper end of the guide so that it subsequently comes into contact with a spinning wheel, so as to continuously manufacture metal fibers. However, the supplied metal rod may abrade the guide and collar as it comes into frictional contact with such guide and collar. As a result, a gap may be formed between the collar and the metal rod. In this case, there are problems associated with process continuity and stability because molten metal may flow through the gap. Furthermore, although the collar and guide temporarily support the molten metal, they still have problems associated with damage thereto by the heat of the molten metal. Where an induction coil having a bowl shape is used, the extracted metal fibers may be stained on the coil. Where an induction coil having a flat plate shape is used, an increased coil installation space of 7 to 8 cm on the average per rod having 1 cm in diameter is required. For this reason, it is impossible to install a sufficient number of rods in one manufacturing apparatus. Thus, it is impossible to provide a manufacturing apparatus with a high productivity.
U.S. Pat. No. 4,157,729 and Korean Patent Nos. 178643 and 190906 registered in the name of the inventors disclose methods and devices for manufacturing metal filaments by heating the entire of a metal rod by a first heating member while heating an end of the metal rod by a second heating member, thereby forming droplets of the melt and forming metal filaments from those droplets using a rotating disk. Since the first heating member is arranged within the second heating member, induced current is generated at the first heating member during a secondary heating process, thereby causing an electrical short circuit or spark. In this case, the manufacturing process cannot be further performed.
When liquid metal of high temperature is rapidly solidified, it may be left on a rotating disk due to its residual stress and chemical affinity without being released from the rotating disk. When such a residual material subsequently comes into contact with molten metal, it destroys the stability of the liquid metal and the process must be stopped. In order to solve this problem, U.S. Pat. No. 5,601,139 proposed use of a cleaning device. However, a wire blush type of cleaning device may damage the surface of the disk when it is used for a prolonged period of time. For this reason, it may be difficult to continuously manufacture fibers of a desired small diameter and the surface of disk blade becomes harsh. In addition, diameter of fiber isn""t uniform.
Therefore, an object of the invention is to provide an apparatus and method for continuously manufacturing metal filaments in mass production by melting only the end of a metal bar in accordance with a high frequency induction heating process in a vacuum device, thereby forming a molten metal maintained, without using any vessel such as crucible, hearth in a state freely depending from the end of the metal bar in accordance with the balance between the weight of the molten metal and the surface tension of the molten metal, and bringing the molten metal into contact with a spinning disk, thereby solidifying the molten metal in the form of fibers having an ingredient uniformity.
In accordance with one aspect, the present invention provides an apparatus for manufacturing metal filaments comprising: metal bar supply assembly including a support member adapted to support a plurality of metal bars, a screw adapted to rotate for a vertical movement thereof by a servo-motor, and a guide rod adapted to guide the screw to carry out an accurate vertical movement, the metal bar support member connecting the metal bars, the screw, and the guide rod, and vertically feeding the metal bars at a speed of 0.1 to 100 mm/min, the metal bar supply assembly being configured to individually control the metal bars; metal bar heating assembly including an induction coil arranged near lower ends of the metal bars, and adapted to a limited part to melt the tip of the metal bars in accordance with a heating operation thereof, a coil block adapted to supply high frequency induction current to heat each of the metal bars to a melting temperature, and a coil cooling water supplier adapted to prevent the induction coil from being melted, the induction coil being upwardly bent in the form of a nose shape at regions thereof where metal filaments are discharged while being soared up, respectively, so as to prevent each molten metal of the metal bars from being affected by the induction coil during soaring of the metal filaments; cooling assembly including a spinning disk provided at a peripheral surface thereof with a plurality of disk blades each having a sharp edge, the spinning disk serving to quench the molten metal at a rate of 104 to 106xc2x0 C./sec while rotating at a linear speed of 1 to 100 m/sec, thereby soaring a metal filament; and wiping assembly including a heat-resistant non-woven fabric adapted to come into direct contact with the spinning disk, thereby removing residual metal materials left on the spinning disk without being released from the spinning disk during the soaring of the metal filaments, and a rotating drum adapted to support the non-woven fabric while enabling a continuous cleaning operation and reducing generation of friction; wherein the metal bar heating assembly, the cooling assembly, and the wiping assembly are arranged in the interior of a vacuum chamber, the molten metal is maintained in the form of a droplet depending from its metal bar by its surface tension without using any particular vessel such as a crucible, hearth, and the soared up metal filaments have a diameter of 10 to 150 xcexcm.
In accordance with another aspect, the present invention provides a method for manufacturing metal filaments comprising the steps of: preparing a metal filament manufacturing apparatus including metal bar supply assembly for supporting a plurality of metal bars, and vertically feeding the metal bars, metal bar heating assembly including an induction coil, a coil block, and a coil cooling water supplier, cooling assembly including a spinning disk provided at a peripheral surface thereof with a plurality of disk blades each having a sharp edge, and wiping assembly including a heat-resistant non-woven fabric, and a rotating drum; forming a vacuum in a chamber in which the metal bar heating assembly, the cooling assembly, the wiping assembly are arranged; supplying a plurality of metal bars at a speed of 0.1 to 100 mm/min by the metal bar supply assembly, thereby arranging the end of each of the metal bars near the induction coil of the metal bar heating assembly, applying electric power to the induction coil, thereby heating and melting a tip of the metal bar, so that molten metal is freely hung at the end of the metal bar in the form of a droplet maintained in a state depending from the end of the metal bar without using any vessel; bring the molten metal into contact with an associated one of the disk blades of the spinning disk rotating at a linear speed of 1 to 100 m/sec, thereby a metal filament having a diameter of 10 to 150 xcexcm while quenching the molten metal at a rate of 104 to 106xc2x0 C./sec; and bring the disk blades of the spinning disk brought into contact with the non-woven fabric attached to the rotating drum of the wiping assembly, thereby removing residual materials or foreign matters firmly attached to the disk blade.